Polyvinylidene fluoride (PVDF) polymers are melt-processable resins that are formed into polymer structures by many different processes, such as extrusion, injection molding, fiber spinning, extrusion blow molding and blown film. They are also used as polymer processing aids due to their low surface energies and phase behaviors. Increasing the PVDF molecular weight is known to increase the melt strength, but often decreases other properties such as the drawdown ratio. Crosslinked PVDF may increase the melt strength, but are limited by the fact that they are not easily processable and often contain a high amount of gels.
High molecular weight PVDF is made on an industrial scale by emulsion polymerization. The highest molecular weight commercial product, KYNAR® 761A (Arkema Inc.) has melt viscosity of 35 kp and a solution viscosity of 350 cp in 7.5% NMP and 25° C. The highest molecular weight PVDF made at industrial scale via suspension polymerization, KF-7200 Kureha) has solution viscosity of about 1900 cp in 7.5% NMP at 25° C.
Surprisingly it has now been found that a fluoropolymer having ultra-high molecular weight can be made and processed, and the physical properties exhibited by the ultra-high molecular weight materials are far beyond those expected merely by the large increase in molecular weight.